Mo—Cu pseudoalloys possess properties that are similar to the properties of W—Cu pseudoalloys. However, they have the additional advantages of lower weight and higher workability which makes them better suited for miniaturized electronics.
One conventional method for making articles comprised of Mo—Cu pseudoalloys consists of infiltrating separately sintered porous molybdenum blanks with liquid copper. Infiltrated articles have a solid molybdenum skeleton that functions as the backbone of the pseudoalloy. The skeleton retains the liquid copper during infiltration (and high temperature operation) by capillary forces. One drawback of the infiltration method is that it does not allow near-net or net-shape fabrication of parts. Hence, a number of machining operations are required to obtain the final shape of the infiltrated article.
Other conventional methods for forming Mo—Cu articles include consolidating blends of molybdenum and copper powders by powder metallurgical (P/M) techniques such as hot pressing, explosive pressing, injection molding, tape forming, and rolling. Unlike the infiltration method, these methods do not have a separate step for sintering a molybdenum skeleton. As a result, articles made by P/M methods either completely lack a molybdenum skeleton or have a skeleton of reduced strength. High compacting pressure, repressing, resintering, and sintering under pressure (hot pressing) have been suggested to improve Mo—Mo contacts and the strength of the Mo skeleton. Although P/M techniques allow near-net or net-shape fabrication, sintering articles to full density is complicated by the lack of solubility in the Mo—Cu system, poor wetting of molybdenum by copper, and by copper bleedout from parts during sintering. Furthermore, additions of sintering activators such as nickel and cobalt to improve densification are detrimental to the thermal conductivity of Mo—Cu pseudoalloys, a property which is critical for a number of electronics applications.
In order to improve the homogeneity and density of Mo—Cu pseudoalloys made by P/M methods, Mo—Cu composite powders have been used wherein the molybdenum particles have been coated with copper by chemical deposition or electroplating. However, the copper coating reduces the contact area between molybdenum particles and the strength of the molybdenum skeleton. Moreover, these powders do not prevent copper bleedout from parts during sintering, and hot pressing is still required to improve the sintered density of articles. Thus, it would be advantageous to have a Mo—Cu composite powder which could be used in P/M methods to form net or near-net shaped Mo—Cu articles having strong sintered molybdenum skeletons without copper bleedout.